Technical Field
Embodiments of this disclosure generally relate to a laminate-type power storage element that houses a power generating element in an exterior body formed of laminated films and a manufacturing method of the power storage element.
Related Art
As a form of a power storage element such as a primary battery, a secondary battery, and an electric double layer capacitor, there has been provided a laminate-type power storage element that seals a flat plate-shaped electrode body together with electrolytic solution in a flat-bag-shaped exterior body formed of laminated films. Since the laminate-type power storage element easily achieves both a large capacity and downsizing and thinning and is also excellent in heat radiation performance, the laminate-type power storage element has been conventionally used as a power supply for driving an electric vehicle, a hybrid vehicle, or a similar vehicle. Recently, utilizing the feature of being easily downsized and thinned, the laminate-type power storage element has been used as a power supply for an extremely thin electronic device (hereinafter, a thin electronic device) that incorporates a power supply, such as an IC card with a one-time password function and a display, an IC card with display, a tag, and a token (one-time password generator). Especially, an external dimension of a card type electronic device (card electronic device) compliant to a standard for IC card is specified by the standard, and the thinness is extremely thin, 0.76 mm. Therefore, the laminate-type power storage element is indispensable as a power supply for the card electronic device.
FIGS. 1A and 1B illustrate a general laminate-type power storage element. FIG. 1A is an external view of a laminate-type power storage element 1, and FIG. 1B is an exploded perspective view illustrating an outline of an internal structure of this power storage element 1. As illustrated in FIG. 1A, the laminate-type power storage element 1 has a flat plate-shaped appearance. An exterior body 11 formed of laminated films shaped into a flat rectangular bag internally seals a power generating element. In the laminate-type power storage element 1 illustrated here, distal end parts (24, 34) of a positive electrode terminal plate 23 and a negative electrode terminal plate 33 are guided in an identical direction from one side 13 of the rectangular exterior body 11.
Next, the following describes a schematic structure of the laminate-type power storage element 1 with reference to FIG. 1B. FIG. 1B hatches some members and portions for easy distinction from other members and portions. As illustrated in FIG. 1B, the exterior body 11 internally seals an electrode body 10 together with electrolytic solution. The electrode body 10 is formed by laminating a sheet-shaped positive electrode 20 and a sheet-shaped negative electrode 30 via a separator 40. The positive electrode 20 is formed by disposing a positive electrode material 22 containing a positive-electrode active material over one principal surface of a positive electrode current collector 21 made of a metal plate and a metal foil. The negative electrode 30 is formed by disposing a negative electrode material 32 containing a negative-electrode active material over one principal surface of a negative electrode current collector 31 made of a metal plate, a metal foil, or a similar material. The electrode body 10 is configured by laminating and press-bonding the positive electrode 20 and the negative electrode 30 such that the respective electrode materials (22, 32) are opposed via the separator 40 (or being welded to the separator 40). In this example, electrode terminal plates (23, 33), which are formed of a strip-shaped metal plate, metal foil, or similar material, are mounted to the respective electrode current collectors (21, 31) of the positive electrode 20 and the negative electrode 30. Further, the tab lead 2 is used as the electrode terminal plates (23, 33). As is well known, the tab lead 2 is structured such as using insulating resin sealing material (hereinafter, tab film 4) adhered in a manner sandwiching the terminal lead 3 on a portion of the extending strip-like terminal lead 3 that is made of such as a metal plate or a metal foil that are substantially the electrode terminal plates (23, 33). And one end portions 5 of the terminal leads 3 are exposed to the outside of the exterior body 11 as the distal end parts (24, 34) of the positive electrode terminal plate 23 and the negative electrode terminal plate 33. The other end portions are coupled to a part of the positive electrode current collector 21 and a part of the negative electrode current collector 31 by such as ultrasonic welding.
The exterior body 11 is configured by welding peripheral edge regions 12, which are hatched or indicated by the dotted line frame in the drawing, of two rectangular laminated films (11a, 11b), which are stacked to one another, by thermocompression bonding to seal the inside. As is well-known, the laminated films (11a, 11b) have a structure where one or more resin layers are laminated on front and back of a base material made of such as aluminum foil. Generally, the laminated films (11a, 11b) have a structure where a protecting layer made of, for example, a polyamide resin is laminated on one surface and an adhesive layer with thermal weldability made of, for example, a polypropylene is laminated on the other surface. When assembling the laminate-type power storage element, the two laminated films (11a, 11b) are made to oppose each other with the adhesive layer side facing inside and the electrode body 10 is disposed between the two laminated films (11a, 11b). Then the peripheral edge regions 12 of the mutual laminated films (11a, 11b) are thermocompression bonded to form a flat-bag-shaped exterior body 11. The tab films 4 of the tab leads 2 are thermowelded together with the laminated films (11a, 11b) on the edge side 13 to which the electrode terminal plates (23, 33) protrude on the peripheral edge region 12 of the exterior body 11 during the thermocompression bonding. Hereby, the tab films 4 welded to the terminal lead 3 are welded to the adhesive layer of the laminated films (11a, 11b) at this edge side 13.
Since the laminate-type power storage element is used as the power supply for electronic devices, the electrode terminal plates need to be coupled to an electronic circuit in the electronic device to incorporate the laminate-type power storage element into the electronic device. In other words, the laminate-type power storage element needs to be implemented to the substrate (circuit board) of the electronic circuit. Soldering, ultrasonic welding and the like can be given as methods for implementing the laminate-type power storage element. However, solder thickness control during soldering is difficult. When the laminate-type power storage element is used in for example, the above card electronic device, the solder may become thick at the implementation region so that the laminate-type power storage element may not be able to be incorporated into the card electronic device. On the other hand, the thickness of the implementation region would not present an issue with ultrasonic welding, since the electrode terminal plates themselves are directly welded to the predetermined print wiring part on the circuit board. However, since ultrasonic welding is associated with ultrasonic vibration caused by a large amount of energy creating frictional heat that melts the contact surface between the electrode terminal plates and the print wiring, the electrode terminal plates may be damaged or disconnected, depending on circumstances, in cases where the electrode terminal plates are formed with thin metal foils. Therefore, a method using an anisotropic conductive film (hereinafter also referred to as an ACF) has been widely employed as an implementation method for the laminate-type power storage element. As is well known, an ACF is a film-shaped component having a predetermined thickness used for implementation, and has a conductive property only in the thickness direction.
FIGS. 2A to 2D are schematic drawings illustrating the method to implement the laminate-type power storage element 1 illustrated in FIGS. 1A and 1B to an electronic circuit board using the ACF. FIGS. 2A to 2D illustrate the implementation procedure. FIGS. 2A to 2D are enlarged views in a cross section viewed from arrow a-a in FIG. 1A and illustrates a region near the electrode terminal plates (23, 33). First, as illustrated in FIG. 2A, the distal ends (24, 34) of the electrode terminal plates (23, 33) are guided to the outside of the exterior body 11 in the assembled laminate-type power storage element 1. The positive electrode terminal plate 23 and the negative electrode terminal plate 33 are disposed separately in a direction orthogonal to the plane of the paper in the drawing. As illustrated in FIG. 2 B, a single ACF 70 is interposed between a power feeding terminal pad 61 and respective surfaces of the distal end sides (24, 34) of the electrode terminal plates (23, 33) of the positive electrode 20 and the negative electrode 30 (hereinafter also referred to as implementation surfaces 50). The power feeding terminal pad 61 is formed as a print wiring on a circuit board 60 such as a flexible printed circuit board (FPC) constituting the electronic circuit. That is, the one ACF 70, which extends in the direction orthogonal to the plane of the paper, is bridged across both electrode terminal plates (23, 33). As illustrated in the drawing, the implementation surfaces 50 of the electrode terminal plates (23, 33) are disposed to be lower surfaces and the relative up-down direction in the electrode terminal plates (23, 33) is specified. Then, as illustrated in FIG. 2C, the thermocompression bonding is performed from top surfaces (hereinafter also called back face 51) of the electrode terminal plates (23, 33) with, for example, a block-shaped jig 80 with a built-in heater. As illustrated in FIG. 2D, this couples the electrode terminal plates (23, 33) of the two positive and negative electrodes to the power feeding terminal pad 61 on the circuit board 60 via the one ACF 70.
The thickness of the implementation region can be kept stable with the implementation method using ACF and the electrode terminal plates would not be damaged with this method since vibration of the electrode terminal plates is not required, which is different from the case of ultrasonic welding. And the laminate-type power storage element can be implemented to the circuit board by the thermocompression bonding process having a sufficiently large coupling strength and a sufficiently small coupling resistance.
For example, Non-Patent Literature 1 (FDK CORPORATION, “Thin Type Primary Lithium Batteries,” [online], [searched on Jan. 4, 2016], Internet <URL: http://www.fdk.co.jp/battery/lithium/lithium_thin.html> (<URL: http://www.fdk.com/battery/lithium_e/lithium_thin.html> in English)) describes a structure of the ACF, the implementation method using the ACF, or similar information. For example, Japanese Unexamined Patent Application Publication No. 2006-281613 discloses the structure of the laminate-type power storage element or similar information. The above Non-Patent Literature 1 describes features, discharge performance, and a similar specification of the thin lithium batteries, actually commercially available laminate-type power storage elements.
To implement the laminate-type power storage element to the electronic circuit using the ACF, in accordance with the up-down direction illustrated in FIG. 2B to FIG. 2D, the jig is pressed against the electrode terminal plates from above to couple the electrode terminal plates to the circuit board via the ACF. That is, the ACF is heated via the electrode terminal plates made of metal excellent in thermal conductivity. The ACF is thermally welded to the terminal pad or a similar member on the circuit board. And the jig that comes into contact with the top surfaces of the electrode terminal plates may reach up to a temperature of 200° C. during the thermocompression bonding. Hereby, the heat of the jig is transmitted to the electrode body inside the exterior body via the electrode terminal plates, possibly damaging the electrode body by a so-called temperature shock. In particular, the laminate-type power storage element used as the power supply of a small-sized thin electronic device represented by a card type electronic device has a high possibility of having the electrode body damaged by the heat of the jig rapidly transferring to the entire area of the small electrode body inside the exterior body via the electrode terminal plates during thermocompression bonding the ACF.
Thus as described in Non-Patent Literature 1, there is a laminate-type power storage element called a support-type laminate-type power storage element which has one of the two laminated films that configure the exterior body extended to the distal end regions of the electrode terminal plates. FIGS. 3A to 3C illustrate this support-type laminate-type power storage element 1s. Similar to FIGS. 2A to 2D, the up-down direction is defined with the side of the implementation surfaces 50 of the electrode terminal plates (23, 33) facing the downward direction and the front-rear direction is defined with the direction in which the electrode terminal plates (23, 33) are guided outside as the front direction, in the following. The direction that is orthogonal to both the up-down and the front-rear directions is defined as the right-left direction, where each of the right and the left directions are designated when viewed from the front toward the rear, as illustrated in FIGS. 3A to 3C. FIG. 3A is an external view of the support-type laminate-type power storage element is seen from above, FIG. 3B is a perspective view of the support-type laminate-type power storage element 1s seen from below and FIG. 3C is a drawing enlarging a part proximate the electrode terminal plates (23, 33) of a cross section viewed from arrow b-b in FIG. 3A.
As illustrated in FIGS. 3A to 3C, the support-type laminate-type power storage element is has the locations of the front margins (13a, 13b) from which the electrode terminal plates (23, 33) are guided outside differentiated at the respective laminated films (11a, 11b) that face each other. In the example illustrated in FIGS. 3A to 3C, the lower laminated film 11b, similar to a common laminate-type power storage element 1 illustrated in FIGS. 1A and 1B, has the front margin 13b thereof located where the electrode terminal plates (23, 33) are guided outside, whereas the upper laminated film 11a has the front margin 13a thereof located at a position that covers the entire region where the electrode terminal plates (23, 33) are formed. In other words, the upper laminated film 11a extends up to a location such that the entire region where the electrode terminal plates (23, 33) are formed is covered by the right and left margins 14. And a rectangular region (hereinafter also referred as support tab 15) that alone covers the back faces 51 of the electrode terminal plates (23, 33) is formed to the front margin 13b of the lower laminated film 11b. The electrode terminal plates (23, 33) and the ACF 70 are thermocompression bonded from above the support tab 15 as illustrated in FIG. 4 when implementing this support-type laminate-type power storage element 1s. Hereby, the electrode terminal plates (23, 33) do not come into direct contact with the jig 80 thereby keeping the temperature of the electrode terminal plates (23, 33) from rapidly rising and enabling the electrode body 10 from being damaged.
By the way, the support tab 15 is a part of the laminated film 11a and the side thereof that faces the back faces 51 of the electrode terminal plates (23, 33) has formed thereto an adhesive layer that melts by heat. And during thermocompression bonding, the adhesive layer of the support tab 15 comes into contact with the back face 51 of the electrode terminal plates (23, 33) and heat concentrates on the metal electrode terminal plates (23, 33) as well. Therefore, the region of the adhesive layer of the support tab 15 that comes into contact with the electrode terminal plates (23, 33) during thermocomporession bonding melts faster than the other regions so that the melting of the adhesive layer may reach up to the surface layer of the metal foil, which is the base of the laminated film 11a. When the adhesive layer of the laminated film 11a melts up to the surface layer of the metal foil in the region where the adhesive layer of the of the laminated film 11a comes into contact with the back faces 51 of the electrode terminal plates (23, 33), it is a matter of course that an external short-circuit would be developed between the electrode terminal plates (23, 33) of the positive electrode 20 and the negative electrode 30.
It is therefore an object of the present invention is to provide a laminate-type power storage element that does not have the electrode body damaged by a thermocompression bonding process and can certainly keep a short circuit from being generated between the electrode terminals, and a manufacturing method of the laminate-type power storage element.